Use of interleukin-2 (IL-2) and IL-2 activated lymphocytes (LAK) has been proposed as a promising approach for the immunotherapy of cancer. Currently, LAK are defined functionally by the characteristics of in vitro requirement for IL-2 activation and specificity of lysis to natural-killer resistant fresh tumor cell populations. Preliminary results concerning the disease regression in patients receiving LAK therapy are inconclusive, but intriguing. Although the LAK system shares some aspects in common with that of NK and CTL, LAK are considered distinct based on a variety of characteristics including kinetics of activation, stimulus responsible for activation heterogeneous phenotype of precursor and effector cells, and specificity of lysis directed toward fresh autologous tumor cells and for modified self. While the current understanding of the LAK system is extremely primitive, extensive studies of human LAK in vitro at the precursor, activation, and target specificity areas as proposed in this project are expected to complement each other and lead to an increased understanding of the immune system as directed to cancers as well as to resolving the immunotherapeutic potential of the LAK system. LAK are generated by incubation of PBL with recombinant IL-2 (no tumor needed) for at least 3 days at 37 degrees C in standard tissue culture medium. Our first aim is to prepare monoclonal antibodies to the p75 IL-2 receptor LAKpre, in order to determine whether a unique functional cell type can be identified. Mice are immunized with LAKpre enriched PBL, and immune spleen cells fused with NS-1. And if available, the resulting MoAb will be used to purify LAKpre for application in research on the mechanism of activation and specificity of lysis. Irrespective of MoAb availability, analysis of the mechanism by which IL-2 alone appears to activate the cytolytic program of LAKpre is a second aim. We will determine minimal components needed for activation in serum free conditions; these minimal conditions will then be used to determine the effect(s) of other biologic response modifiers and cells that might be regulatory in vivo (lymphokines, regulatory lymphocytes, autochtonous tumor cell). Our third aim is to characterize the tumor cell surface component(s) responsible for susceptibility to LAK lysis. We will build on our original finding of a trypsin-sensitive site, and test the enzyme sensitivity of known proteoglycan and other glycoprotein structures in relationship to LAK sensitivity.